City Hall has given Joanna Lumley's controversial £175m Garden Bridge final planning approval.
London mayor Boris Johnson delegated the final decision to a deputy after publicly supporting the project.
The trust behind the project needs to find a further £65m before the project can start. It must also guarantee annual funding of £3.5m to pay for running costs
City Hall says construction work could begin next year if the money is raised. Critics complain the bridge will wreck historic views of the Thames, there is no right of way and access will be restricted.
The Garden Bridge Trust says construction will start Autumn 2015 with opening due Summer 2018.